The invention relates to apparatus for use in a developer station where charge images formed on a charge image carrier passed through the developer station are inked in accordance with magnetic brush principles with a developer mix of toner and carrier particles.
Typically non-mechanical printing or copying machines function according to electrophotographic principles, wherein electrostatic latent images of characters to be printed are generated on a recording medium, such as a photoconductive drum. The drum has on it a semi-conductor layer of photo-electrical or di-electrical material on which electrostatic charge images of the characters to be printed or copied are generated. These electrostatic images are subsequently inked with a toner powder, usually a black powder, in a developer station. The toner images are subsequently transferred to sheet paper on which they are fixed. The developer station typically includes at least one developer unit generally referred to in the art as a magnetic brush developer. The magnetic brush developer, as a rule, contains a magnetic brush or drum mounted for rotation so as to continually bring developer mix, consisting of iron carrier particles and toner particles, into contact with the electrostatic images recorded on the photoconductive drum surface. The charge images are inked by adherence of toner particles to the charge images, due to electrostatic forces.
A developer station assembly which functions in accordance with magnetic brush principles is disclosed in U.S. Pat. Nos. 3,784,297 and 3,883,240. There, developer mix is conducted past the revolving surface of a photoconductive drum carrying the charge images to be generated by means of two rotating magnetic or developer drums. A developer mixing device, including two side-by-side rotary screws disposed along the floor of the developer station housing in intimate contact with the supply of developer mix, is provided to continuously distribute the toner and carrier particles of the mix and blend in fresh toner added to the main body of mix to make up for toner spent in the charge image inking process.
A significant problem, especially with respect to high-speed copying and printing machines, is that of developing or inking the latent charge images on the charge image carrier simultaneously along the entire width of the carrier with consistent inking densities throughout developer operation and high resolution. This requires a high level of effective performance in the developer station since typical high-speed image carriers pass charge images through the developer station at speeds up to 0.7 m/sec. Furthermore, it is necessary to guarantee that only the charge images are inked. A sporadic, unintentional spotting or otherwise contamination of the charge image carrier surface with clumps of toner or entrained toner deposits must be avoided. Despite all of these requirements, the developer station in a high-speed printer or copying machine must also operate reliably over time such that servicing is only rarely necessary to eliminate frustrating and inefficient downtime.
An object of the present invention is to provide a developer station with apparatus such that, even in the case of high-speed printers or copiers, charge images on the charge image carrier are consistently and reliably inked uniformly over the entire width of the carrier with constant inking densities and high resolution and contamination of the background areas on the charge image carrier due to spotting is avoided with a high degree of certainty.